Microstrip antenna structure

Abstract

A microstrip antenna structure is provided wherein a plurality of relatively narrow elements, resonant in their longer dimensions, are organized into two staggered or offset sets of interleaved elements with each set being fed from opposite sides of the structure through a corporate microstrip feed line from a common feed point. The aligned radiating ends of the two offset sets of elements simulate four line sources of radiation. The preferred embodiment produces an efficient end-fire radiation pattern from this relatively compact structure which may, in turn, constitute an individual end-fire radiator in a larger array structure.

What is claimed is: 
     
       1. An antenna structure, said structure comprising: an electrically conductive ground plane surface,   a layer of electrically conductive radiator elements having respectively corresponding feed line elements connected thereto,   a dielectric substrate having a predetermined thickness disposed between said ground plane surface and said layer,   said radiator elements comprising a first set of spaced apart radiators having respectively associated resonant axes directed in a first direction away from the connection of said feed line elements respectively associated therewith and a second set of spaced apart radiators having respectively associated resonant axes directed in a second direction opposite to said first direction away from the connection of said feed line elements respectively associated therewith,   the indvidual radiators of said first and said second sets of spaced apart radiators being interleaved, and   said feed line elements being connected between a common feed point and the individual ones of said radiator elements to provide electrical signals thereto in a transmit mode and to receive electrical signals therefrom in a receive mode said electrical signals having predetermined relative phase relationships for producing a correspondingly predetermined antenna response pattern.   
     
     
       2. An antenna structure as in claim 1 wherein said layer comprises a unitary and integral electrically conductive layer shaped to define said radiator elements and said feed line elements. 
     
     
       3. An antenna structure as in claim 1 wherein: said first and second sets of spaced apart radiators comprise individual radiators having a first dimension along their respective resonant axes and a second dimension substantially perpendicular thereto,   said first dimension being substantially equal to a first predetermined distance in terms of wavelength of the electrical signals in the dielectric substrate at a predetermined operating frequency and also substantially equal to a second predetermined distance in terms of wavelength of the electrical signals in the area overlying said radiators at said predetermined operating frequency,   said first and second sets of spaced apart radiators being interleaved to a depth substantially equal to a third predetermined distance in terms of wavelength of the electrical signals in the area overlying said radiators at said predetermined operating frequency,   said first, second and third predetermined distances in terms of wavelength having a predetermined relative relationship.   
     
     
       4. An antenna structure as in claim 1 wherein: the distances from said common feed point along said feed line elements to each of the individual radiators in the first set of spaced apart radiators are equal to a first dimension,   the distance from said common feed point along said feed line elements to each of the individual radiators in the second set of spaced apart radiators are equal to a second dimension, and   said first and second dimensions differ by a predetermined number of quarter wavelengths of the electrical signals in the dielectric substrate at a predetermined operating frequency.   
     
     
       5. An antenna structure comprising a plurality of individual structures as in claim 1 disposed in an array of such individual structures. 
     
     
       6. An antenna structure as in claim 1 wherein said feed line element connections to said radiator elements comprise an electrical connection at the outer perimeter of each of said radiator elements along a side intersected by its respectively associated resonant axis. 
     
     
       7. An antenna structure as in claim 6 wherein said feed line elements comprise a corporate structured microstrip feed line. 
     
     
       8. An antenna structure, said structure comprising: an electrically conductive ground plane surface,   a layer of electrically conductive radiator elements having respectively corresponding feed line elements connected thereto,   a dielectric substrate having a predetermined thickness disposed between said ground plane surface and said layer,   said radiator elements comprising a first set of spaced apart radiators having respectively associated resonant axes directed in a first direction and a second set of spaced apart radiators having respectively associated resonant axes directed in a second direction opposite to said first direction,   the individual radiators of said first and said second sets of spaced apart radiators being interleaved,   said feed line elements being connected between a common feed point and the individual ones of said radiator elements to provide electrical signals thereto in a transmit mode and to receive electrical signals therefrom in a receive mode said electrical signals having predetermined relative phase relationships for producing a correspondingly predetermined antenna response pattern,   said first and second sets of spaced apart radiators comprising individual radiators having a first dimension along their respective resonant axes and a second dimension substantially perpendicular thereto,   said first dimension being substantially equal to a first predetermined distance in terms of wavelength of the electrical signals in the dielectric substrate at a predetermined operating frequency and also substantially equal to a second predetermined distance in terms of wavelength of the electrical signals in the area overlying said radiators at said predetermined operating frequency,   said first and second sets of spaced apart radiators being interleaved to a depth substantially equal to a third predetermined distance in terms of wavelength of the electrical signals in the area overlying said radiators at said predetermined operating frequency,   said first, second and third predetermined distances in terms of wavelength having a predetermined relative relationship, and   said first predetermined distance being one wavelength and said second predetermined distance being one-half wavelength and said third predetermined distance being one-fourth wavelength.   
     
     
       9. An antenna structure as in claim 8 wherein said dielectric substrate has a relative dielectric constant of substantially 4. 
     
     
       10. An antenna structure as in claim 8 wherein said dielectric substrate has a relative dielectric constant between 2 and 6. 
     
     
       11. An antenna structure as in claim 8 wherein said second dimension of said radiators is greater than approximately one-tenth wavelength of the electrical signals in the area overlying said radiators at said predetermined operating frequency. 
     
     
       12. An antenna structure as in claim 11 wherein the interleaved individual radiators are spaced one from another by a distance which is at least approximately said predetermined thickness dimension of said dielectric substrate. 
     
     
       13. A microstrip antenna structure for transmitting or receiving electromagnetic radio frequency signals at at least one predetermined operating frequency, said antenna structure comprises: an electrically conductive ground plane surface;   a dielectric substrate overlying said ground plane, said dielectric substrate having a predetermined thickness and a predetermined relative dielectric constant;   a plurality of substantially rectangularly shaped electrically conductive radiator elements overlying said dielectric substrate;   said rectangular radiator elements having substantially parallel longitudinal axes along respective length dimensions which are resonant at said operating frequency in said dielectric substrate;   said plurality of rectangular radiator elements comprising a first set of elements having first and second radiating ends substantially aligned respectively along first and second lines in the transverse or width dimensions thereof and a second set of elements having third and fourth radiating ends substantially aligned respectively along third and fourth lines in the transverse or width dimensions thereof;   the individual elements of said first and second sets being interleaved and offset with respect to each other so as to sequence said lines in the respective order of first, third, second and fourth,   a common feed point, and   a corporate structured microstrip electrically conductive feed line extending from the common feed point to the radiating ends of said first set disposed along said first line and also extending from the common feed point to the radiating ends of said second set disposed along said fourth line, the distances along the feed line from said common feed point to the individual elements of the first set differing from the distances along the feed line from said common feed point to the individual elements of the second set by a predetermined amount.   
     
     
       14. An antenna structure as in claim 13 wherein said plurality of radiator elements and said feed line comprise a unitary and integral electrically conductive layer shaped to define said radiator elements and said feed line. 
     
     
       15. An antenna structure as in claim 13 wherein said predetermined amount of difference in the feed line lengths is substantially equal to a predetermined number of quarter wavelengths at said operating frequency in said dielectric substrate. 
     
     
       16. An antenna structure comprising a plurality of individual structures as in claim 13 disposed in an array of such individual structures. 
     
     
       17. An antenna structure as in claim 13 wherein said length and width dimensions, said offsetting said feed line distances and said predetermined relative dielectric constant are adapted to cooperate in effectively simulating the overall effect of four line radiation sources corresponding to said first, third, second and fourth lines with the correct line source spacing and relative phasing to produce an end-fire radiation pattern for said antenna structure. 
     
     
       18. An antenna structure as in claim 13 wherein said length dimensions are substantially equal to one wavelength at said operating frequency in said dielectric substrate. 
     
     
       19. An antenna structure as in claim 18 wherein said predetermined relative dielectric constant is between 2 and 6. 
     
     
       20. An antenna structure as in claim 18 wherein said first, second, third and fourth lines are spaced from one another at intervals substantially equal to one-fourth wavelength at said operating frequency in the space above said radiator elements. 
     
     
       21. An antenna structure as in claim 20 wherein said predetermined relative dielectric constant is substantially 4. 
     
     
       22. An antenna structure as in claim 13 wherein the center-to-center spacing between radiator elements of said sets is greater than approximately two-tenths wavelength at said operating frequency in the space above said radiator elements and less than approximately one-half wavelength. 
     
     
       23. An antenna structure as in claim 22 wherein adjacently located radiator elements are spaced apart by a distance which is at least approximately said predetermined thickness dimension of said dielectric substrate.